Ion gauge



April 21, 1953 F. c. HURLBUT ION GAUGE Filed May 26, 1,950

Patented Apr. 21, 1953 UNITED STATES PATENT" OFFICE ION. GAUGE Franklin0. H'urlliut, Berkeley, Califi, assignor to The Regents-"of theUniversity of California, Berkeley; Calilc, a" corporation ofCalifornia.

ApplicationMay 26, 1950,.S'erialN'o. 164,451

2' Claims. 1 My invention. relates to means especially useful inconnection with evacuated. vessels and vacuum processes in general toserve as. a. measuring device.

Ion gages. in. general are. well known and depend for their operation.upon. thev conduct. of electrical charges at subatmospheric pressure.Ordinarily available gages. are subject to. variations inaccuracy fromtime. to time and are especially subject to inaccuracies due to. changesin the gage structure occurring during protracted use- It is thereforean object of my invention to provide an improved ion gage.

Another object of my invention is to provide an ion gage which can.readily be utilized with sub-atmospheric vacuum equipment of thecustomary kind.

A still-further object-of. my invention is to provide a vacuum gage inwhich protracted operation does not seriously aifect the working nor theaccuracy of theinstrument.

A still further object of my invention is to provide means forpreventing erratic results. due to sputtering'of the filament material.

A still further object of my invention isto provideanion gagemechanicallyarranged and disposed in such a fashion that-it has a highinitial accuracy which is maintained throughout substantially the entireuseful lifeof the gage;

Other objects, together with the foregoing, are attained in theembodiment of the invention described in the accompanying descriptionand illustrated in the accompanying drawings, in which Figure l is aplan of a portion of an ion gage constructed in accordance with myinvention.

Figure 2 is a cross section, the plane of which is indicated by the line2-2 of Figure 1.

Figure 3 is a cross section, the plane of which is indicated by the line3-3 of Figure 2.

In its preferred form, the ion gage of my invention is inclusive of anenvelope evacuable through a tubular connection, the envelope preferablybeing of substantially drum shape with the tube connection in oneportion of the cylindrical side wall. The two, substantially planar,opposite end walls, are equipped with lead buttons so that the filament,the grid and the anode of the tube are all appropriately supported. Thearrangement is such that the anode lead buttons are on the opposite wallfrom the grid and filament lead buttons and the arrangement is likewisesuch that sputter shields are interposed between each of the variouslead buttons and the filament.

While the ion sage of my invention is. susceptible to variousmodifications depending partly upon the environment: in which it is'to'be utilized and. depending, in part, upon other factors, it hassuccessfully been embodied and operated as shown herein.

In. this. form of the device, an access tube 6 is provided with arestriction 1 in the customary fashion and leads to a coupling 8 inwhich is mounted a standard outgassing. bypass valve 9 and athermocouple lfl' passing. through terminals II and [2. Most of thestructures so far described are standard parts of auxiliary appaa ratusand are fabricated of metal. The ion gage of my invention preferablycommences with a metallic ferrule l3 adapted to be connected by a bandof solder I 4 to the remaining metallic members and including a taperedconnection l6 incorporating; a standard metal. to lass seal; forexample, a copper to glass seal.

Secured thereby to the ferrule I3 is an envelope [8' preferably ofglass. or comparable material, the. envelope being essentially. circularin cross section in one plane and substantially rectangular in. cross.section in the other plane so that it is. generally of drum. shape.Fromthe connection [6,, a flare l9 merges. with the cylindrical wall 2 Iofthe envelope 18. The. envelope is substantially symmetricalon oppositesides of. the flare. l9 and at its opposite ends is closed by a firstwall 22 and" by a parallel wall 23, these walls being, fun,-d'amentall'y planar and perpendicular to the general cylindrical axis ofthe envelope I8.

Approximately in the center of the first wall 22, I provide a filamentsupport post 24 which may be imbedded in but preferably does not extendentirely through the wall 22. Within the envelope I8 the supportincludes an offset leg 26 leading to a central terminus 21 on theopposite side of the envelope so that a close approach to wall 23 ismade.

At appropriate points in the wall 22 and preferably symmetricallydisposed with respect to the central mounting 24, are a pair of filamentlead buttons 28 and 29, respectively. Each of these buttons is inclusiveof a protrusion 3| from the envelope of approximately conical contourand also is inclusive of a metallic conductor 32 extending through thematerial of the envelope from an external termination, available forconnection in a circuit, to an internal terminus. The two filament leadbuttons 28 and 29 serve as diametrically opposite supports for afilament wire 33 extending from points adjacent to the wall 22 acrossthe central portion of the drum envelope to rest upon the filamentsupport 21 3 near the wall 23. Thus, the filament stretches across orspans the projected axis of the ferrule IS The wall 22 is additionallyprovided with a pair of symmetrically arranged grid lead buttons 35 and31 each of which is of a construction similar to the filament leadbuttons. Within the envelope It, the grid leads are connected to theopposite ends of a helically formed grid structure 38 substantiallyencompassing the entire filament and including a support leg 39.

., ond of said walls, a pair of filament lead buttons The opposite wall23 of the envelope I8 is pro- 1 those elements and occupying a positionrelatively close to the wall 2i of the envelope.

In addition to the mentioned parts, in the interior of the envelope,preferably on each of the lead buttons such as 28 and 29, and 36 and 31,as well as 4| and 42, sputter shields 41 are disposed. These areconstituted of discs of suitable material forced over the leads as theyemerge from the buttons to lie adjacent the interior surface of theenvelope each in a location substantially intersecting all direct linesof communication from the filament to the envelope adjacent therespective lead button.

In the operation of this device, the interior of the envelope [8 isappropriately evacuated and the various lead connections are made sothat the filament 33 is energized. The customary electron travel occursand the gage is utilized in the usual Way to afford ion concentrationreadings. Especially important is the fact that emanations from thefilament in the nature of small metallic particles which normally areconducting and which tend to coat the interior of the envelope and shortcircuit or cause leakage or drainage currents from the variousconductors passing through the envelope, are substantially entirelyintercepted. This is especially true near the open ends of the anode.While the sputter shields 41 may themselves eventually be coated withconducting material on the side toward the filament, the other sideremains a good non-conductor. The sputter shields in effect shade orshadow the various lead buttons so that the interior of the envelopeadjacent to the conducting parts of the lead buttons is kept free of onsaid first wall, a filament connected to said filament lead buttonsextending across said envelope and resting on said support, a pair ofgrid lead buttons on said first wall, a grid connected to said grid leadbuttons and encompassing said filament, and extending across saidtubular connector, a pair of anode lead buttons on said second wall, ananode connected to said anode lead buttons and encompassing said grid,and disclike sputter shields on each of said lead buttons disposedparallel to said planar walls and out of contact with said envelope andshading said buttons from said filament.

2. An ion gage comprising a non-conducting envelope of drum shape havinga pair of opposite planar walls and a tubular connector in theintervening cylindrical wall, filament and grid supports in one of saidplanar Walls, an anode support in the other of said planar walls, afilament and a grid on their respective supports within said envelope, ahelical anode on said anode supports surrounding said filament and saidgrid and close to said cylindrical wall, and sputter shields on saidsupports adjacent both of the open ends of said anode and spaced fromsaid envelope and interposed between said filament and the portions ofsaid envelope carrying said supports.

FRANKLIN C. HURLBUT.

References Cited in the file of this patent UNITED STATES PATENTS

